Radial bearing with a sliding bearing-type construction

ABSTRACT

The invention relates to a radial bearing which can be used for bearing problems in which an angular displacement occurs during operation by virtue of the elastically flexible shaping of a bearing sleeve on which an elastically flexible bearing element with an essentially matrix-type fibrous structure is arranged.

BACKGROUND OF THE INVENTION

The invention relates to a radial bearing of the sliding-bearing type,in particular for use in centrifugal pumps, with a bearing sleevearranged on a rotating shaft part and designed to transmit torque, thebearing sleeve being arranged rotatably within a bearing bush, and a gapfor a low-viscosity lubricating medium being located between the partssliding on one another.

Various embodiments of shaft mountings are known in centrifugal pumps,different bearing materials being used, depending on the feed medium.Ceramic bearing materials have proved particularly advantageous inbearings which are lubricated with a low-viscosity feed medium, forexample with water or alcohol. A disadvantage of ceramic bearings ofthis type is their sensitivity to overheating due to deficientlubrication and jolt-like loads. Such sensitivity occurs in the regionof mixed friction, for example when the sliding faces touch one anotheras a result of radial loads which are too high. At the same time,thermal-stress cracks may be formed within the ceramic due to anexcessive local introduction of frictional heat into the ceramicsurfaces. This gives rise to the risk of local pronounced materialoverload, with the result that cracks or spalling occur on the ceramicpart and consequential damage is to be expected.

An additional load acts on such a mounting consisting of a stationarybearing bush and of a rotating bearing sleeve, when an angular offsetarises between these parts. For example, it is known from DE-A-1528640,in such mountings, to arrange the bearing bush elastically relative to ahousing by means of O-rings, in order to achieve easy moveability.

In the case of large multi-stage pumps or long shafts with bearingsarranged between them, for example in large feed pumps, borehole shaftpumps or cantilevered mountings with a shaft overhang on one side,inclinations or deflections of the shaft occur as a result of the forceswhich prevail during operation. As a result, the bearing sleeve rotatingtogether with the shaft likewise assumes an inclination. A one-sidedbearing load resulting from this constitutes a further risk to ceramicbearings which are sensitive to impact or jolt loads.

SUMMARY OF THE INVENTION

The problem on which the invention is based is, therefore, to develop ashaft mounting which uses break-sensitive materials and which allows anangular offset occurring in the mounting.

This problem is solved in that the bearing sleeve consists of a carryingelement and of a bearing element fastened to the latter, in that afibrous structure arranged predominantly in a matrix-like manner andhaving ceramic particles or carbon particles arranged in it forms thebearing element, in that a ceramic or carbon matrix forms the fibrousstructure, in that the carrying element is provided with different wallthicknesses in the region of bearing contact of the bearing element, andin that the carrying element is designed to be equal to or longer thanthe bearing element.

As seen in longitudinal section, the carrying element has awall-thickness profile which is at a maximum in the middle region and isconfigured to decrease from the latter toward both sides. The ceramic orcarbon-containing bearing element having a predominant matrix-likefibrous structure is pressed with a shrink fit or press fit onto thecarrying element. The dimensions and tolerances of the individual partsare selected such that, under the effects of temperature, the bearingelement remains firmly connected to the carrying element. Thecombination of such a bearing element with a carrying element havingelasticity affords the advantage that, when an angular offset occurs,the two parts react in an elastically resilient manner and therefore therisk of a break on the bearing element is prevented. In contrast to amonolithic component, the fibrous structure, which is arranged in apredominantly matrix-like manner and is designed as a ceramic or carbonmatrix into which ceramic or carbon particles are embedded, hasresilience with respect to bending loads. At the same time, depending onthe desired bearing pairing, both ceramic particles and carbon particlesmay be arranged in a carbon matrix. The same also applies to a ceramicmatrix.

Thus, a property more resistant to tensile stresses occurring underbending loads can be produced on such bearing elements which are per sebreak-sensitive and are made as sintered parts. The tensile stressesoccurring under bending load in a sleeve cross section of such a bearingelement and risking a break are improved by the factor 10, as comparedwith a pure sintered material, by means of the fibers arranged in amatrix-like manner. The angular deviations of the mounting canconsequently be compensated.

If the bearing element is connected to the carrying element by means ofa shrinkage connection, the shrinkage forces of the bearing elementcause the formation of a slightly convex shape in the assembled state.Since, according to one embodiment of the invention, the carryingelement has a substantially smaller wall thickness in the region inwhich the ends of the bearing element are located than in the middleregion of the latter, the shrinkage forces cause a reduction in diameterin the region of the smaller wall thicknesses. A shrunk-on bearing bushwith its fibrous structure composed predominantly in a matrix-likemanner, for example consisting of silicon carbide fibers or carbonfibers, therefore has a slightly convexly formed surface which isconducive to the compensation of angular deviations of a shaft mountingequipped with it. The combination of the bearing element equipped with amatrix-like fibrous structure with the carrying element, the shape ofwhich leads to a spring characteristic curve about the radial axis,ensures an elasticity which compensates angular errors. In the case ofpressed-on bearing elements, only the elastic resilience ensures thecompensation of angular deviations.

Further embodiments of the invention are described in the subclaims. Thefeature whereby the end faces of the carrying element project beyond theend faces of the bearing element reduces the occurrence of stress peaksand allows the spring characteristic curve to be influenced positively.By virtue of a free space being arranged between the shaft and thecarrying element in the region of one or both end faces of the bearingelement, space is provided for the elastic compensation of angularerrors.

The carrying element and the bearing element fastened to it form therotating part of the radial bearing, the bearing sleeve. In a middleregion of the bearing element, the carrying element has a wall-thicknessmaximum, the dimensions being selected such that reliable forcetransmission is thereby ensured. Furthermore, the region of thewall-thickness maximum serves for receiving means transmittingrotational movements between the shaft and carrying element.Wall-thickness minima are provided on the carrying element in the regionof the end faces of the bearing element. These minima are conducive tothe spring effect of the carrying element and to the formation of aconvex shape of the bearing face.

At least one thick-walled end portion led up to the shaft may beprovided in the region of the end faces of the carrying element, thisend portion being arranged at a distance from the end face of thebearing element. In between, the wall of the carrying element isdesigned as an elastically resilient thin-walled portion. Thethick-walled end portion arranged in the region of the end face of thecarrying element may also have torque-transmitting or force-transmittingdesigns. For the bearing contact of the bearing element, the carryingelement may have an end-face bearing surface.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the invention are illustrated in the drawings and aredescribed in more detail below. In the drawings:

FIGS. 1-3 show various embodiments of the carrying element,

FIG. 4 shows the arrangement of such a carrying element in a bearingwithout angular offset,

FIGS. 5 and 6 show the arrangement of a carrying element when an angularoffset occurs and an associated carrying diagram, and

FIGS. 7 and 8 show illustrations similar to those of FIGS. 5 and 6 inthe case of a conventionally designed mounting.

FIG. 1 shows, in longitudinal section, a carrying element 1 which may beof a metallic or non-metallic type and which is designed, in the middleregion, as a portion 2 of maximum wall thickness. This portion 2 isdesigned for the transmission of torques and, for this purpose, usesknown means 3, for example tongue-and-groove connections. The wallthickness of the carrying element 1 becomes increasingly smaller fromthe middle portion 2 toward the end faces 4, 5. Such a wall-thicknessprofile has a profile without sharp-edged transitions. Fastened to theoutside diameter of the carrying element 1 is a bearing element 6 whichconsists of a fibrous structure arranged predominantly in a matrix-likemanner, a ceramic or carbon matrix forming the fibrous structure.Ceramic or carbon particles are embedded into the matrix. The axiallength of the bearing element 6 is made equal to or shorter than theaxial length of the carrying element 1. The end faces 7, 8 of thebearing element 6 are arranged so as to be set back relative to the endfaces 4, 5 of the carrying element 1. Such a measure prevents theoccurrence of stress peaks at the transition between these two parts.

The middle portion 2 of the carrying element 1 makes a web-likeconnection to the shaft. Starting from the portion 2, the wall thicknessof the carrying element 1 is configured so as to decrease toward the endfaces 4, 5. Such a shape, which provides a free space between a surface9 of a shaft and the carrying element 1, can be produced in a simpleway, for example by cutting machining.

FIGS. 2 and 3 show other embodiments which likewise ensure elasticproperties of a bearing sleeve formed in this way. They may be used inthe case of higher radial forces to be absorbed. The axial length of thecarrying element 1 is increased, as compared with the embodiment of FIG.1. In this case, the region of the end faces 4, 5 of the carryingelement 1 was designed in such a way that an approximation to thesurface 9 of a shaft, not illustrated, is made.

In FIG. 2, the surfaces 10, 11, located opposite the shaft surface 9, ofthe end faces 4, 5 of the carrying element 1 are arranged so as to forma gap. There is therefore the possibility of influencing a deflection ofthe carrying element 1, taking place under the influence of radialforces, by means of the clearance shown between the surfaces 10, 11 andthe surface 9. By suitable selection of the dimensions for a clearancefit to be provided between these parts, it is possible in a simple wayto limit deflection. A thin-walled portion 12, 13 of the carryingelement 1, said portion being arranged between the end faces 7, 8 of thebearing element 6 and the end faces 4, 5 of the carrying element 1,ensures the resilience properties of a bearing sleeve, formed in thisway, of a radial bearing. It is possible to produce a progressive springcharacteristic curve by means of such a measure.

The illustration of FIG. 2 depicts on the right-hand side, in the regionof the end face 4, a different profile of that end of the carryingelement 1 which is located opposite a face 11 of the shaft surface 9.The transition 13 is depicted as being conical here, but othertransitions in the form of arcs or the like are also possible. Such aconfiguration is advantageous during the mounting of such a bearing andmakes it possible to introduce it more easily. In the illustration ofFIG. 2, the end face 5 on the left-hand side is designed in such a waythat the carrying element can be pushed over the means 3 necessary fortorque transmission.

The modification of FIG. 3 provides torque-transmitting means 3 solelyin the region of the end face 5 of the carrying element 1. In order totransmit the bearing forces acting on the bearing element 6, thecarrying element 1 rests in the region 2, with the faces 10, 11, on thesurface 9 of a shaft. It is essential, in this case, that there be athin-walled portion 12, 13 between the end faces 7, 8, limiting thelength of the bearing element 6, and the faces 10, 11 of the carryingelement 1. As can also be seen in FIG. 2, such a portion ensures theresilience of such a unit.

The embodiments of FIGS. 1 to 3 show an identical length of the bearingelement 6, but the invention is not restricted to these. Theiradvantages may also be achieved by means of other overall lengths of thebearing element 6.

FIG. 4 shows a mounted bearing version, using as an example thecomponent of FIG. 1. A carrying element 1 is arranged on a shaft 14 soas to transmit torque by virtue of the means 3. A bearing element 6shrunk onto the carrying element 1 cooperates with a bearing bush 15. Itis shown how the end-face thin-walled ends of the carrying element 1acquire a convex shape under the influence of the shrinkage forces andrun toward the shaft 14. Furthermore, in conjunction with thewall-thickness profile which becomes thinner in the direction of the endface, elastic resilience becomes possible, thus ensuring theprecondition for compensating an angular offset of the shaft 14 inrelation to the bearing bush 15.

FIGS. 5 and 6 show a radial bearing according to the invention duringthe compensation of angular deviations. FIG. 5 shows a bearing sleevewhich is inclined at the angle β relative to a stationary bearing bush15 and consists of the carrying element 1 and bearing element 6 andwhich rotates together with a shaft 14. The accompanying perspectiveillustration of FIG. 6, a top view of a bearing sleeve deformed underthe action of force, shows a large contact face 16. This is producedbetween the bearing bush 15 and the bearing element 6. As a result ofthe bearing element 6 assuming a convex shape which is formed underload, the deformation leads, in the case of a slight inclination, to anadaptation of the sliding faces resting against one another. By thebearing face 16 being enlarged, along with the same radial force, localsurface pressure acting on the bearing element 6 is reduced to aconsiderable extent. Consequently, a radial bearing designed in this wayis substantially less sensitive to jolt-like, impacting and frictionalloads than a bearing consisting of rigid elements.

FIGS. 7 and 8 show a mounting according to the prior art in a similarway to the illustration in FIGS. 5 and 6. In the case of an angularoffset β of a monolithic ceramic bearing sleeve 18, only the very narrowbearing face 17 shown in FIG. 8 is afforded when inclination occurs. Incomparison with large-area bearing contact of the faces during operationwithout any inclination, an inclination causes a considerable reductionin the bearing face normally present. The radial force acting on thebearing is therefore distributed to a substantially smaller area.Consequently, the surface pressure acting on the bearing element and/orthe local frictional output exceeds the permissible values. Themonolithic bearing sleeves, used hitherto for such mountings, in theform of ceramic materials which, because of their break sensitivity,should not be either shrunk on or otherwise put under tensile stress,are overloaded in such an operating situation. Their intended use istherefore restricted considerably.

What is claimed is:
 1. A radial bearing in the form of a frictionbearing comprising a bearing sleeve arranged on a shaft and designed totransmit torque, said bearing sleeve being arranged rotatably within abearing bush, and said bearing being provided with a gap for alow-viscosity lubricating medium between parts which slide on oneanother; said bearing sleeve comprising a support element and a bearingelement attached to the support element; said bearing element comprisinga fibrous ceramic or carbon matrix structure having ceramic or carbonparticles disposed therein; said support element having varying wallthicknesses where it is attached to the bearing element, and saidsupport element having a length at least equal to the bearing element.2. A radial bearing according to claim 1, wherein said support elementis longer than the bearing element and has axial end faces which projectaxially beyond axial end faces of the bearing element.
 3. A radialbearing according to claim 2, wherein at least one free space isprovided between said support element and a shaft surface adjacent theend faces of the bearing element.
 4. A radial bearing according to claim2, wherein said support element has a wall thickness which decreasesfrom a maximum thickness in a central region thereof toward the axialend faces of the bearing element.
 5. A radial bearing according to claim4, wherein said support element has a region of maximum wall thicknessadjacent a central region of said bearing element.
 6. A radial bearingaccording to claim 3, further comprising force transmitting elementsarranged in said central region of said support element.
 7. A radialbearing according to claim 4, wherein said support element has regionsof minimum wall thickness adjacent the axial end faces of said bearingelement.
 8. A radial bearing according to claim 1, wherein said supportelement has a thin-walled portion between each axial end face of thebearing element and a thick-walled axial end portion of the supportelement.
 9. A radial bearing according to claim 1, wherein said bearingelement lies against an axial surface of said support element.
 10. In acentrifugal pump, the improvement comprising a radial bearing accordingto claim 1.